#
# * This program is free software; you can redistribute it and/or modify
# * it under the terms of the GNU General Public License version 2 as
# * published by the Free Software Foundation;
# *
# * This program is distributed in the hope that it will be useful,
# * but WITHOUT ANY WARRANTY; without even the implied warranty of
# * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# * GNU General Public License for more details.
# *
# * You should have received a copy of the GNU General Public License
# * along with this program; if not, write to the Free Software
# * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

# Network topology
#
#       n0    n1   n2   n3
#       |     |    |    |
#       =================
#              LAN
#
# - UDP flows from n0 to n1 and back
# - DropTail queues
# - Tracing of queues and packet receptions to file "udp-echo.tr"

try:
    from ns import ns
except ModuleNotFoundError:
    raise SystemExit(
        "Error: ns3 Python module not found;"
        " Python bindings may not be enabled"
        " or your PYTHONPATH might not be properly configured"
    )


def main(argv):
    #
    # Allow the user to override any of the defaults and the above Bind() at
    # run-time, via command-line arguments
    #
    cmd = ns.core.CommandLine()
    cmd.Parse(argv)

    #
    # But since this is a realtime script, don't allow the user to mess with
    # that.
    #
    ns.core.GlobalValue.Bind(
        "SimulatorImplementationType", ns.core.StringValue("ns3::RealtimeSimulatorImpl")
    )

    #
    # Explicitly create the nodes required by the topology (shown above).
    #
    print("Create nodes.")
    n = ns.network.NodeContainer()
    n.Create(4)

    internet = ns.internet.InternetStackHelper()
    internet.Install(n)

    #
    # Explicitly create the channels required by the topology (shown above).
    #
    print("Create channels.")
    csma = ns.csma.CsmaHelper()
    csma.SetChannelAttribute("DataRate", ns.network.DataRateValue(ns.network.DataRate(5000000)))
    csma.SetChannelAttribute("Delay", ns.core.TimeValue(ns.core.MilliSeconds(2)))
    csma.SetDeviceAttribute("Mtu", ns.core.UintegerValue(1400))
    d = csma.Install(n)

    #
    # We've got the "hardware" in place.  Now we need to add IP addresses.
    #
    print("Assign IP Addresses.")
    ipv4 = ns.internet.Ipv4AddressHelper()
    ipv4.SetBase(ns.network.Ipv4Address("10.1.1.0"), ns.network.Ipv4Mask("255.255.255.0"))
    i = ipv4.Assign(d)

    print("Create Applications.")

    #
    # Create a UdpEchoServer application on node one.
    #
    port = 9  # well-known echo port number
    server = ns.applications.UdpEchoServerHelper(port)
    apps = server.Install(n.Get(1))
    apps.Start(ns.core.Seconds(1.0))
    apps.Stop(ns.core.Seconds(10.0))

    #
    # Create a UdpEchoClient application to send UDP datagrams from node zero to
    # node one.
    #
    packetSize = 1024
    maxPacketCount = 500
    interPacketInterval = ns.core.Seconds(0.01)
    client = ns.applications.UdpEchoClientHelper(i.GetAddress(1).ConvertTo(), port)
    client.SetAttribute("MaxPackets", ns.core.UintegerValue(maxPacketCount))
    client.SetAttribute("Interval", ns.core.TimeValue(interPacketInterval))
    client.SetAttribute("PacketSize", ns.core.UintegerValue(packetSize))
    apps = client.Install(n.Get(0))
    apps.Start(ns.core.Seconds(2.0))
    apps.Stop(ns.core.Seconds(10.0))

    ascii = ns.network.AsciiTraceHelper()
    csma.EnableAsciiAll(ascii.CreateFileStream("realtime-udp-echo.tr"))
    csma.EnablePcapAll("realtime-udp-echo", False)

    #
    # Now, do the actual simulation.
    #
    print("Run Simulation.")
    ns.core.Simulator.Stop(ns.Seconds(10))
    ns.core.Simulator.Run()
    ns.core.Simulator.Destroy()
    print("Done.")


if __name__ == "__main__":
    import sys

    main(sys.argv)
